Circuit interrupting device



April 23, 1945. B. w. JONES Erm` 2,399,037

CIRCUIT INTERRUPTING DEVICE Filed March 11, 1943 Inventors: A Benjamin W. Jones,

Otto R. Schurg,

Their- Attorneg.

Patented Apr. 23, 1946 2,399,037 CIRCUIT INTERRUPTING DEVICE Benjamin W. Jones and Otto R. Schurig, Schenectady, N. Y., assignors to General Electric Company, a 4corporation of New York .implication` March 11, 1943, Serial No. 478,784

(Cl. 20G-120) 6 Claims.

Our invention relates to circuit interrupting devices and more particularly to circuit interrupting devices employing a fusible element and used for protecting electrical apparatus of. the liquid insulation filled type such as motor start ers, transformers and the like.

Electrical apparatus, such as Vmotor starters, transformers and the like often comprise a caring or container filled with an insulating dielectric such as oil or the like. In .order topprotect such apparatus, it would .be .desirable to provide devices which could be mounted Iwithin the container or casing, preferably immersed in the dir-` electric which devices are simple and inexpensive, and would operate to give complete protection to the apparatus under` both moderate and high overload conditions. y

Our invention is particularly concerned with a new `and improved oil immersedfuse and has for its principal object such a fuse embodying the featuresenumerated above. I

It is another object of our invention to provide a new and improved fuse of the .oil immersed type which operates von the oil blast principle and effectively interrupts the current under both moderate and high overload conditions.

Further objects and advantages of our invention will become apparent `as the following description proceeds and the features of novelty which characterize `our linvention will be pointed out with particularity in .the claims annexed to and forming a part; of this specification.

For a better understanding of our invention, reference may be had to the accompanying drawm ing in which Fig. 1 is a schematic diagram partly in section illustrating an application of oil immersed fuses embodying our invention, Fig. 2 is an enlarged view partly in section of a fuse emu .bodying our invention, Fig, 3 is a sectional view taken `on line 3-3 of Fig. 2, Fig. 4 is a sectional View taken yon line 4--4 of Fig. 2 Fig. 5 is a partial view of the fuse of Fig. 2 taken along line 5-5 of Fig. 2 and Fig. 6 is a sectional view of a fuse showing a modincation of our invention.

Although the circuit interrupting device of our invention is applicable for protecting any liquid insulation lled type of apparatus, we have chosen to illustrate it in Fig. 1 yas applied to oil immersed contactor generally indicated at Il?. Oil immersed contacter I0 comprises a `casing il filled with an insulating dielectric such as oil I2. Mounted within casing I I is a contacter schematicallyxindicated at I3. Contacter .I3 may be a single phase or a polyphase apparatus, protected by one or more fuses I4 embodying ourv invention.

kper or the like.

One fuse I4 is connected in series with `each phase of the contacter and these fuses are completely immersed in oil as indicated in Fig. l.

The .oil immersed fuses I4 of Fig, l may take the form `illustrated in Figs. 2 to 5, comprising an insulating casing I5. At the upper end of casing I5 is an upper fuse terminal I6. Similarly, at the lower vend of casing I5 is a lower fuse terminal Il. Each of these terminals` I and `I'I are provided with an opening I8 so that electrical connections by bolting or the like ,be made with associated circuits vas indicated in Fig. l.' The construction of upper and lower fuse terminals I6 and II forms no part of our inven tion and may comprise any suitable form which` will permit ready assembly with casing I5. In order to hold the terminals in position at the ends of casing I5 we provide upper and lower terminal caps I9 and 2l) respectively which are each provided With a central opening 2I through which fuse terminals I6 and I'I may extend.

Inter-connecting fuse terminals I6 and Il is a fuse link generally indicated at 22. Fuse link 22 is provided with an upper fusible element 23 and a lower fusible element 24 each provided `with one or more portions of reduced cross-section 25 indicated best in Fig. 5. Under high overload conditions the fuse link 22 will rupture at one of these portions of reduced cross-section to interrupt the circuit therethrough. Fuse links of this type have a fairly high melting temperature well above the lowest temperature at which an insulating dielectric such as `oil is damaged or decomposed and under low overload current con ditions when the rate of heating is slow, diiliH culties would be encountered in melting this link preparatory to interrupting the circuit. To thi-,eI end our new and improved fuse link 22 comprises a central section which includes a pair of conducting members such as upper member 25 and lower member 2'I preferably constructed of cop- The upper member 26 is connected by suitable means as indicated at 2B with the upper fusible element 23 while the lower member 21 is connected by similar means 28 with lower fusible element 24. The adjacent ends of the members 26 ,and 2l are soldered together as indicated at 29. Preferably this solder has a relatively low melting point compared to the ten:- perature .at which the fusible elements 23 24 of fuse link 25 will rupture. However, the mass of members 26 and 2l are large so to conductl heat away from solder 29 and the 1neltingtime of solder 29 may be controlled by a proper proportioning of vthe-associated parts.

In order to cause high speed separation of the adjacent ends of the members 2B and 21 upon melting of the solder 29, we have provided means including a spring 30 which enga-ges with an insulating pin member 3| suitably fastened to the lower end of upper member 26 and normally extending through an opening 32 in lower member 21 and surrounded by solder 29. Upon melting of the solder 29 spring 30 will force pin 3| to move through the opening 32 in lower member 21 and cause relative separation between members 26 and 21 so as to interrupt the circuit. With this arrangement a sort of time lag feature is provided on moderate overload currents which would not cause the fusible portions 23 and 24 of fuse link 22 to rupture at the restricted portions 25.

In order to be sure that satisfactory interruption of the circuit occurs on relatively high currents, we have discovered that by providing one or more openings 33 in the walls of casing I5 adjacent the restricted portions 25 of fuse link 22, a very effective oil blast action takes place upon rupture of the fuse link. These openings 33 permit the immediate escape of oil and gases from the fuse tube or casing I5 so as to provide an oil blast effect whereby the extinction of the arc is accelerated. We have discovered that these openings should be relatively large to perform satisfactorily with the desired oil blast effect. We have also discovered that in fuses such as have been described above, convection currents cause a high convection effect between the liquid dielectric in the fuse casing I5 and the surrounding dielectric I2 in casing II of Fig. l. This convection effect will tend to cool the fuse link so that the esired operating characteristics are not obtained. We have found that by providing a mechanically weak covering such as a puncturable or frangible closure member over the openings 33 such convection currents are stopped and yet at the same time the escape of oil through the openings as soon as the closure member is punctured upon the occurrence of a moderate pressure within the casing I5 is permitted. By covering the openings 33 the convection currents which would remove heat from the fusib-le element so rapidly that an abnormally high wattage would be required to bring the fuse link to its melting point at moderate overload currents is prevented.

These closure members might take any suitable form and as illustrated in the drawing may comprise a wrapping 34 of cloth, paper, or some equivalent material. We have illustrated these closure members as a complete wrapping around i the casing l5 but it should be understood that small puncturable closure members might be provided for each individual opening so long as they prevent convection currents and yet permit an effective oil blast action.

A small bleed hole l1 is provided in lower fuse terminal I1 so that under normal current carrying conditions an equalization of pressure inside and outside of casing I5 is permitted. Temperature changes due to normal load current carried by fuse link 22 will therefore not cause an increase of pressure in casing I5 to rupture wrapping 34.

In view of the detailed description included above, the operation of the oil immersed fuse of our invention. will be obvious and no further discussion thereof will be included hereinafter.

In Fig. 6 we have illustrated a fuse I 4 which is a modification of our invention which modification goes only to the terminals of the fuse and the fuse link itself. These have been designated with the same reference numerals as in Fig. 2 marked with a prime. The other corresponding parts of Fig. 6 are, furthermore, designated with the same reference numerals as in Fig. 2. Fusible link 22 of Fig. 6 comprises two fusible elements 35 and 36 respectively including portions of reduced cross-section 31 which are mounted opposite oil blast openings 33 so as to operate in the same manner as the fuse described above. The fusible elements 35 and 36 of :fuse link 22 are soldered together by a low melting point solder 38 substantially identical with the low melting point solder 29 of Fig. 2. The elements 35 and 36 respectively are provided with spring biasing members 39 and 4u constantly tending to bias these members apart so as to assume the dotted positions indicated in Fig. 6. Under moderate overload conditions the solder 38 will eventually melt so as to cause separation of the fuse link parts 35 and 36 with the consequent interruption of the current flowing therethrough. Under high overcurrent conditions, on the other hand, the fuse link 22 will rupture at one of the restricted portions 31 and the arc drawn will be rapidly extinguished by the oil blast action similar to that described in connection with the fuse I4 of Fig. 2.

From the above description it will be obvious that we have provided a new and improved oil immersed fuse which will operate very effectively both at high and low currents. Furthermore, this fuse is simple and compact and readily adaptable for use with apparatus such as oil immersed contactors, transformers or the like.

While we have described preferred embodiments of our invention, it will be obvious to those skilled in the art that various changes may be made without departing from our invention and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What We claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric fuse of the type adapted to be immersed in a liquid insulating dielectric such i as oil and capable of interrupting satisfactorily both high and low currents comprising a casing, a pair of terminals associated with said casing, a fuse link interconnecting said terminals comprising a restricted portion adapted to rupture upon high overcurrents and a soldered joint adapted to melt after a time delay upon moderate overcurrents, and means comprising an opening in said casing adjacent said restricted portion of said fuse link to permit an oil blast action to interrupt the current flowing in said fuse upon rupture of said fuse link at said restricted portion.

2. In an electric fuse of the type adapted to be immersed in a liquid insulating dielectric such as oil and capable of interrupting satisfactorily both high and low currents comprising a casing. a pair of terminals associated with said casing, a fuse link interconnecting said terminals comprising a restricted portion adapted to rupture upon high overcurrents and a soldered joint adapted to melt after a time delay upon moderate overcurrents, means comprising an opening in said casing adjacent said restricted portion of said fuse link to permit an oil blast action to interrupt the current flowing in said fuse upon rupture of said fuse link at said restricted portion, and means for preventing said insulating dielectric from circulating through said opening to cool said fuse link under normal operating conditions.

3. In an electric fuse of the type adapted to be immersed in a liquid insulating dielectric such as oil and capable of interrupting satisfactorily both high and low currents comprising a casing, a pair of terminals associated with said casing, a fuse link interconnecting said terminals comprising a restricted portion adapted to rupture upon high overcurrents and a soldered joint adapted to melt after a time delay upon moderate overcurrents, means for causing separation of said soldered joint upon melting thereof to interrupt the current flowing through said fuse, and means comprising an opening in said casing adjacent said restricted portion of said fuse link to permit an oil blast action to interrupt the current ilowing in said fuse upon rupture of said fuse link at said restricted portion.

4. In an electric fuse of the type adapted to be immersed in a liquid insulating dielectric such as oil and capable of interrupting satisfactorily both high and low currents comprising a casing, a pair of terminals associated with said casing, a fuse link interconnecting said terminals comprising a restricted portion adapted to rupture upon high overcurrents and a soldered joint adapted to melt after a time delay upon moderate overcurrents, spring means for causing separation of said soldered joint upon melting thereof to interrupt the current flowing through said fuse, and means comprising an opening in said casing adjacent said restricted portion of said fuse link to permit an oil blast action to interrupt the current flowing in said fuse upon rupture of said fuse link at said restricted portion.

5. In an electric fuse of the type adapted to be immersed in a liquid insulating dielectric such as oil and capable of interrupting satisfactorily both high and. low currents comprising a casing,

a pair of terminals associated with said casing, a fuse link interconnecting said terminals comprising a restricted portion adapted to rupture upon high overcurrents and a soldered joint adapted to melt after a time delay upon moderate overcurrents, means for causing separation of said soldered joint upon melting thereof to interrupt the current flowing through said fuse, means comprising an opening in said casing adjacent said restricted portion of said fuse link to permit an oil blast action to interrupt the current flowing in said fuse upon rupture of said fuse link at said restricted portion, and means for preventing said insulating dielectric from circulating through said opening to cool said fuse link under normal operating conditions.

6. In an electric fuse of the type adapted to be immersed in a liquid insulating dielectric such as oil and capable of interrupting satisfactorily both high and low currents comprising a casing, a pair of terminals associated with said casing, a fuse link interconnecting said terminals comprising a restricted portion adapted to rupture upon high overcurrents and a soldered joint adapted to melt after a time delay upon moderate overcurrents, spring means for causing separation of said soldered joint upon melting thereof to interrupt the current flowing through said fuse, means comprising an opening in said casing adjacent said restricted portion of said fuse link to permit an oil .blast action to interrupt the current flowing in said fuse upon rupture of said fuse link at said restricted portion, and means for preventing said insulating dielectric from circulating through said opening to cool said fuse link under normal operating conditions.

BENJAMIN W. JONES. O'I'IO R. SCHURIG. 

